BY DR. LAUDER BRUNTON. 



to matters which concern pure chemistry, it may be merely 

 stated that the artificial urea, which can now be readily pur- 

 chased, is prepared' by mixing, in certain proportions, aqueous 

 solutions of potassium cyanate and ammonium sulphate, eva- 

 porating to dry ness and extracting the residue with alcohol. 

 During the process ammonium cyanate is first formed, and sub- 

 sequently this is transformed into its isomer, urea. In order to 

 determine the chief reactions of urea, perform the following 

 experiments : 



/ 1. Take a crystal of urea, and placing it in a water-glass add , . 

 ji, few drops of distilled water. It will dissolve with great ^ 

 readiness. Take a couple of drops of the solution and 

 it to crystallize on a glass slide, which may be gently heated. 

 A residue is obtained which presents to the naked eye a_crys,- 

 talline appearance, and which under the microscope is seen to 



jbe formed of transparent tour-sided prisms, terminated by one 



lor two oblique facets (Fig. 322). 



/ 2. Place a fragment of urea on the tongue, and observe that 

 it possesses a cool, nitre-like taste. 



3. Heat a fragment of urea on a piece of platinum foil, or on 

 a platinum spatula, over a gas or spirit-lamp. The urea will 

 I first melt, then solidify, and ultimately burn away rapidly 

 without leaving a trace of ash or unburned carbon. 



A 4. Place a tiny crystal of urea on a glass slide ; dissolve it 

 /in distilled water, and then add a drop of strong and perfectly 

 colorless nitric acid. Crystals will form which consist of a 

 compound of nitric acid and urea (CH 4 N,O,HNO 3 ). These 

 much less soluble than crystals of urea. Nitrate of urea is ^ 

 comparatively insoluble in dilute nitric acid. Nitrate of urea 

 crystallizes generally in the form of six-sided tables (Fig. 323). 

 From highly concentrated urine ^ma~n,large quantities of 

 nitrate of urea may be sometimes obtained, without any pre- 

 vious evaporation, by merely adding pure nitric acid. In any 

 case, however, nitrate of urea may be obtained in a crystalline 

 form by evaporating urine nearly to a syrupy consistence, de- 

 canting the liquid from the salts which have separated out, and 

 then adding an equal volume of pure nitric acid. 



5. Perform an experiment similar to the preceding one, 

 substituting a solution of oxalic acid for the nitric acid. A 

 crystallization of oxalate of urea (CH 4 N 1 J C t H t O 4 ) is obtained 

 (Fig. 324). 



- 6. Take one cubic centimetre of a solution of pure urea (con-A 

 tainingS grammes dissolved in 100 grammes of distilled water). \ 

 Then add cautiously a solution of mercuric nitrate; a curdy 

 white precipitate forms, which consists of combinations of urea 

 with mercuric oxide. On adding a drop of the mixture of urea I 

 and mercuric nitrate to a drop of a cold saturated solution oT I 

 strdhr-carboirate no reaction will be observed until an excess of 



